690 



THE NERVOUS SYSTEM. 



dentatum ; others come from the cortex and probably also from the smaller nuclei 

 in the central white substance. The majority of the fibres decussate with those 

 of the opposite peduncle below the corpora quadrigemina, and pass to the red 

 nucleus of the tegmentum, from which a relay is prolonged through the optic 

 thalamus to the cerebral cortex. Fibres also connect the spinal cord with the 

 cerebellum through its superior peduncles ; these are chiefly derived from the 

 antero-lateral ascending cerebellar tract of Growers. 



The Valve of Vieussens or Superior Medullary Velum. Stretched across from 

 one superior peduncle to the other is a thin, transparent lamina of white matter, 

 the valve of Vieussens ; on to the dorsal surface of its lower half the folia of the 

 lingula are prolonged. It forms Avith the superior peduncles the roof of the upper 

 part of the fourth ventricle, and is continuous with the central white stem of the 

 cerebellum. It is narrow above, where it passes beneath the corpora quadri- 

 gemina, and broader below, at its connection with the white substance of the 

 superior worm of the cerebellum. A slight elevated ridge descends upon the upper 

 part of the valve from between the lower corpora quadrigemina, and on either side 

 of this may be seen the fourth nerve. 



Anterior 



crescent ic lobe. 



V ' 



Ala lobuli centralis. 



Lingula. 



Superior peduncles 

 of cerebellum. 



Great 



horizontal 



fissure. 



Amygdala. 



Nodule. Fourth ventricle. 



FIG. 366. Sagittal section of the cerebellum, near the point of junction of the worm with the hemisphere. 

 (Schafer.) 



The middle peduncles are the largest of the three pairs. They consist of a 

 mass of curved fibres, which, as already described, comprises most of the trans- 

 verse fibres of the pons. They enter the cerebellum between the margins of the 

 great horizontal fissure at the anterior notch, and the fibres spread out in all 

 directions : some passing to the upper part, and some to the lower part of the hemi- 

 sphere, while others pass to its middle region. Of the fibres contained in the 

 middle peduncles many are commissural between the two hemispheres of the cere- 

 bellum ; others apparently end in the gray matter ; others have been described as 

 giving fibres to the posterior longitudinal bundle, and through it to the nuclei of 

 the third, fourth, and six nerves. Cajal describes still another set, which have 

 their origin in the gray reticular formation of the pons, and which pass partly into 

 the peduncle of the same side and partly into that of the opposite side. 



The inferior peduncles connect the cerebellum with the medulla oblongata. As 

 the restiform bodies of the latter, they will be described in the sequel. They pass 

 upward and outward, forming part of the lateral wall of the fourth ventricle, and 



